The present invention relates to an image pickup apparatus including an opto-electric converting image pickup element, and, more specifically, to a correction method and a correction circuit for correcting registration.
At present, triple-tube color television cameras employing three image pickup tubes (red tube R, green tube G and blue tube B) have been widely utilized in broadcasting stations and the like. On the other hand, being backed in recent years by rapid developments of a solid-state image pickup element, 3-chip type color television cameras employing solid-state image pickup device instead of the image pickup tube have been commonly used.
In the case where three image pickup devices (either image pickup tubes or solid-state image pickup elements) are utilized, if registrations of respective color images are not sufficient (will be shortly referred to as a "registration discrepancy"), positions of the images contained in the television signal will be different from each other with respect to each color. Color blurring phenomenon results resolution is lowered. Therefore, the image quality is deteriorated. Under these circumstance, the pattern images of the respective pickup tubes, or pickup devices of both the multi tube type and multi plate type color television cameras must be registered at a higher precision.
It should be noted that one of causes of a registration error is lens aberration. The amount of aberration varies by a distance measured from a center, a color of light, a zooming ratio, an amount of diaphragm, a distance measured from a subject, and so on. In the camera employing a solid-state image pickup device circuit for reducing the aberration as shown in FIG. 1 has been proposed (Japanese Laid-open Patent Application No. 61-89790 and Japanese Laid-open Patent Application No. 61-89791).
In FIG. 1, incident light has been slit into three colors R, G, B via a lens 1 and a prism 2, and three color lights are converted into electric signals (referred to as "color signals" by image pickup devices) Sr', Sg', and Sb' and output therefrom. FIG. 2 illustrates both a position (referred to as a "position of an arranged element") 7 at a light receiving plane of the image pickup device, for obtaining the output signal in this case, for instance, the output signal Sr' shown in FIG. 1, and also another position 8 of a real image having a registration error caused by a setting error of the image pickup device and the color aberration of the lens. The image position that must be focused onto the position "a" of the arranged element by way of the ideal optical error, is positionally shifted to the point "a'" due to the registration error. An amount of light at this point a' is detected and when the detected light amount is handled as an amount of light at the point "a", the above-described registration error can be corrected. However, as apparent from the drawing, the point a' is not always present on the position of the arranged element.
Therefore, the conventional correction of the registration error with respect to such an output signal represented in FIG. 1 is carried out as follows. That is, several lines of the output signals Sr' (within 1 field) are once stored in a video signal memory 4. In a memory and calculator of a discrepancy of registration 5, the value obtained at a predetermined registration discrepancy position a' is acquired by interpolation values of four element points (1,1) to (2,2) adjacent to the first-mentioned point a' as represented in FIG. 2, and an interpolation signal obtained by this internal calculation is used as a signal of a corresponding correct arranged element position "a", and thus a color signal Sr a discrepancy of registration of which has been corrected is output. Thereafter, other color signals Sro, Sgo, and Sbo whose discrepancy of registrations have been corrected in the similar method are supplied to a process encoder circuit 6 so as to be output as a television signal.
In the circuit shown in FIG. 1 since the corrections of the registration discrepancy are added to the signals (1-field signals) output from the respective image pickup elements Sr', Sg' and Sb', the color blurring phenomenon and low resolution can be prevented. However, the conventional apparatus still has the below-mentioned problems.
It should be noted that FIG. 3 illustrates a construction example of a CCD type solid-state image pickup device, reference numeral 9 indicates a photodiode, reference numeral 10 denotes a CCD in a vertical direction, reference numeral 11 represents a CCD in a horizontal direction, and reference numeral 12 is a source follower circuit.
Since the interlace scanning operation is performed in the normal television system, readout of the video signal from the solid-state image pickup devices of the multi plate type camera is carried out as follows. That is to say, as illustrated in FIG. 4a, a mixture signal obtained from two vertical picture elements is alternatively combined with each other such as 1.sub.1 +1.sub.2, and 1.sub.2 +1.sub.3 every 1 screen (1 field) so as to be output. Otherwise, as represented in FIG. 4b, signals obtained from every two picture elements (lines) such as 1.sub.1, 1.sub.3 ;--, and 1.sub.2, 1.sub.4 ; --are alternately read out every 1 screen (1 field).
As a result, the number of the arranged elements contained in 1 screen (1 field) signal is equal to approximately a half of the picture element numbers of the actual pickup device. In accordance with the conventional registration correction circuit shown in FIG. 1, since the interpolation signal is calculated by using only the signals having a small quantity of pixel points, only the pictures having the low improvement in the resolution along the vertical direction are obtained.